The NIH AIDS Research and Reference Reagent Program (Repository) established by the NIAID in 1988 is a unique resource. It acquires critically needed reagents for AIDS-related research (i.e., samples of cell lines, HIV and related viruses, opportunistic infectious agents associated with HIV infections, DNA libraries, DNA clones, antibodies, purified proteins, synthetic peptides, body fluids, and reference standards), and provides these reagents free of charge to qualified investigators worldwide. The Repository encourages collaborative research aimed at standardizing reagents and laboratory techniques. The Repository is a AIDS Collaborating Center of the World Health Organization. Most of the reagents in the Repository are donated and the generosity of donors is gratefully acknowledged. Any commercial use of reagents requires written permission and compensation of reagent donor(s) and notification of the Repository. Contributors of reagents and users of the Repository include scientists from the NIH, academic and non- profit institutions, and from the private sector. Currently, the Repository has 500 registered users of its services and increasing numbers of investigators are citing the reagent donors and Repository as a source of essential reagents in their publications. During the past five years the Repository has provided more than 17,000 reagents to AIDS investigators worldwide. Repository catalogs published, yearly, contain descriptions of reagents, reagent contributors, biological safety information, vendors of AIDS research reagents, and forms necessary to receive and information to contribute reagents. Updates of catalog are provided periodically in the Repository's newsletter.